Free radical polymerization of nonlinear optical side chain methacrylate copolymers in dimethylsulfoxide — an experimental design

Copolymers prepared by free radical initiation of various ratios of two comonomers, 2-[methyl[4-[2-(4-nitrophenyl)ethenyl]phenyl]amino]ethyl 2-propenoic acid ester (C2ANS) and methyl methacrylate (MMA) are used in the fabrication of nonlinear optical (NLO) devices at Hoechst Celanese. Since the production of these polymers is on the kilogram scale, it was important to optimize the reaction condition to maximize the conversion to high molecular weight product. A set of 22 statistically (D-optimal) designed experiments was run where the variables were temperature (55–75° C), ratio of C2ANS to MMA, the 2,2′-azobis[2-methyl-propanenitrile] (AIBN) concentration, and the level of a coupling agent. Initiator concentration, the ratio squared of the monomers, and the temperature are the most important factors for the polymer percent and the polymer yield. The concentration of the coupling agent, the ratio squared of the monomers, and the interaction of the ratio with the coupling agent are the key factors for the polymer molecular weight. Three-dimensional plots of these measured values show that the highest molecular weight polymer, with a 90% or better yield, is obtained at a temperature of 64–68° C for a ratio of 45–46:55–56 C2ANS:MMA using 1 mol% AIBN.